The corrosion of industrial piping and other components such as valves and pumps is a major problem in some industries. The oil industry, in particular, faces severely corrosive environments, with corrosive gases and liquids such as H2S (hydrogen sulfide) at elevated temperatures and pressures. Additionally, these conditions form severe wear and erosion environments. One solution to these issues is to coat a lower grade base material with a high quality coating material having the desired high corrosion and wear-resistant properties. Typically, these types of properties will be found in metal, ceramic and particularly diamond-like carbon coatings.
Stainless steel is one example of a metal alloy that is sometimes coated to improve corrosion resistance. Other expensive specialty alloys, such as Hastelloy and Inconel (both of which are federally registered trademarks of Huntington Alloys Corporation), are commonly used for exhaust piping in not only the semiconductor industry, but in chemical processing industries in general. These alloys exhibit high temperature strength and corrosion resistance. Again, a less expensive base material can be used if a suitable surface coating is applied to the interior surface that is to be exposed to the corrosive environment.
In the application of a corrosion-resistant coating to a pipe or other workpiece, adhesion of the coating material to the workpiece must be considered. For a particular coating material, some base materials more readily adhere to the coating material than others. For example, a coating material of diamond-like carbon (DLC) adheres more readily to smooth stainless steel than to either nickel or a rough surface such as carbon steel. Chemical vapor deposition (CVD) is used in numerous applications in which adhesion and corrosion resistance are critical performance parameters. Historically, adhesion of a coating bonded to a substrate or other workpiece is promoted by careful selection of the activation energy for bonding, selection of temperature, and the application of surface area preparations. Plasma enhanced CVD (PECVD) enables depositing films at reduced temperatures, but the energy delivered by plasma typically is not sufficient to provide the desired level of adhesion.
U.S. Pat. No. 6,664,182 to Jeng describes a method of improving the adhesion between organic, low k layers of a dual damascene process using a shallow ion-implantation process, which is described as making the low k layer more dense and increasing the dangling bonds. The method description is limited to low k layers on semiconductor substrates and not described for DLC coatings on steel substrates, also ion implantation techniques cannot be applied to internal surfaces as they are limited to line-of-sight very low pressure processes. U.S. Pat. No. 5,541,003 to Nagayama et al. describes a method for improving adhesion of a DLC film to substrates such as alloys containing Co, Ni or Fe, which have only a slight affinity for a DLC film, through the use of an intermediate layer consisting of an amorphous mixture of silicon and carbon, formed by a biased PECVD or ionization evaporation technique. This technique, while an improvement over prior approaches, has limitations (e.g., the process is limited to thin films (described for 3 microns DLC), while corrosion or abrasion or erosion resistant films require much thicker layers). For corrosion resistance, thick films are required to prevent any penetration or diffusion of corrosive material through the coating to the substrate. For erosion or abrasion, a thick film is required particularly on a soft substrate (e.g. carbon steel), due to the transfer of energy to the substrate from the impact of a hard particle (e.g. ˜10 GPa quartz) on the surface. This can cause deformation of the soft substrate and fracture of the hard DLC coating. If the coating is thicker then the diameter of the particle, this energy transfer is greatly diminished, preventing fracture of the coating. Still a further limitation is that this technique cannot be applied to interior surfaces of a pipe or other hollow body. While prior approaches operate well in many applications for coating a workpiece, further advances are sought.